Differential effects on nitric oxide synthase, heat shock proteins and glutathione in human endothelial cells exposed to heat stress and simulated diving

Decompression sickness (DCS) may result from damage to the endothelium caused by the gas bubbles formed during decompression and may be related to nitric oxide (NO) production by nitric oxide synthase (NOS). Heat stress prior to diving has been shown to protect animals from DCS, and by simulating this treatment in human endothelial cells (HUVEC) we have shown that a simulated dive performed subsequent to a heat stress potentiated the heat-induced expression of HSP70 and increased the level of the antioxidant glutathione (GSH). Since operational saturation diving is performed at an increased oxygen level, HUVEC have been exposed to heat stress and simulated diving at 40 kPa O(2), comparing the response on HSP70, HSP90 and GSH level to the effects previously observed at 20 kPa O(2). In addition, we wanted to investigate the effect on both endothelial NOS (eNOS) protein and enzymatic activity. The present results showed that a heat stress (45°C, 1 h) decreased the NOS activity and the protein markedly. Hyperoxia (40 kPa) alone or a dive either at 20 or 40 kPa O(2),had no effects on NOS activity or protein. At 40 kPa O(2) a simulated dive after heat stress potentiated the HS-induced HSP70 response, whereas the heat-induced HSP90 response decreased. GSH levels were found to be inversely related to NOS activity and protein expression, and might be explained by a possible post-translational regulation by glutathionylation of eNOS protein. The results add to the limited knowledge of these critical factors in cellular defence mechanisms that can prevent injury during decompression.